Access point and terminal

Abstract

This access point includes a wireless signal processing unit and a management unit. The wireless signal processing unit discretely arranges a plurality of subcarriers for each allocated resource unit (RU) and communicates with a plurality of terminals. The management unit manages information on maximum transmission power for each RU and for each bandwidth to which the subcarriers belong. Prior to communication with a terminal, the wireless signal processing unit transmits, to the terminal, information on the maximum transmission power for each RU and for each bandwidth to which the subcarriers belong.

Description

Access points and terminals

[0001] The embodiments relate to an access point and a terminal.

[0002] A wireless LAN (Local Area Network) is known as a system that wirelessly connects an access point (AP) and a terminal (STA). A wireless LAN allows a terminal located within the communication area of ​​the AP to access a network via the AP.

[0003] The IEEE 802.11ax standard specifies uplink OFDMA transmission (UL-OFDMA). OFDMA is a method that combines orthogonal frequency division multiplexing (OFDM) and frequency division multiple access (FDMA). OFDMA is a transmission method that divides the channel bandwidth allocated to wireless communication into multiple subcarriers. In OFDMA, subcarrier allocation for multiple STAs is performed in units of RUs (resource units), which are groups of subcarriers that make up one channel. By combining this with FDMA, OFDMA can finely change the subcarrier allocation depending on the radio wave conditions of each STA. This enables many-to-one transmission from multiple STAs to an AP, and therefore OFDMA can improve radio wave utilization efficiency compared to OFDM.

[0004] Currently, the need to more reliably ensure successful transmissions from RUs with a small number of subcarriers is being discussed in the IEEE 802.11TGbn standard, which is formulating the next generation of wireless LAN standards. As a method for more reliably ensuring successful transmissions from RUs with a small number of subcarriers, IEEE 802.11TGbn is discussing a provision called DRU (distributed RU), which configures RUs with discretely arranged subcarriers rather than contiguous subcarriers. By using DRUs to reduce the number of subcarriers per unit frequency, it is possible to increase the maximum transmission power per subcarrier compared to conventional OFDMA, and it is expected that the probability of successful transmission will increase.

[0005] Jianhan Liu et al., “UHR Feature to Overcome PSD Limitations: Distributed-Tone Resource Units”, IEEE 802.11-23 / 0037r0, January 2023

[0006] In each country, upper limits on transmission power are set by law, etc. When a DRU is used, these upper limits on transmission power must also be observed.

[0007] The embodiments provide an access point and a terminal capable of performing OFDMA transmission using DRUs with appropriate transmit power.

[0008] An access point according to one aspect includes a radio signal processing unit and a management unit. The radio signal processing unit discretely allocates multiple subcarriers for each allocated resource unit (RU) to communicate with multiple terminals. The management unit manages information on maximum transmission power for each RU and for each bandwidth to which the subcarriers belong. The radio signal processing unit transmits the information on maximum transmission power for each RU and for each bandwidth to which the subcarriers belong to the terminal prior to communication with the terminal.

[0009] According to the embodiment, an access point and a terminal capable of performing OFDMA transmission using a DRU with appropriate transmission power are provided.

[0010] FIG. 1 is a block diagram showing an example of the configuration of a communication system according to an embodiment. FIG. 2 is a block diagram showing an example of the hardware configuration of an AP. FIG. 3 is a block diagram showing an example of the hardware configuration of a terminal. FIG. 4 is a block diagram showing an example of the functional configuration of an AP according to an embodiment. FIG. 5A is a diagram showing a first example of a broadcast frame. FIG. 5B is a diagram showing a second example of a broadcast frame. FIG. 5C is a diagram showing a third example of a broadcast frame. FIG. 6 is a diagram showing an example of RU allocation in OFDMA transmission using a 20 MHz channel. FIG. 7 is a diagram showing the upper limit of the transmission power (transmission power density) in the 6 GHz band specified by the Radio Law of Japan. FIG. 8 is a diagram showing the arrangement of RUs specified in the IEEE 802.11ax / be standard for UL-OFDMA transmission when a 20 MHz channel is used, and the arrangement of RUs when using the DRU concept proposed in IEEE 802.11TGbn. FIG. 9 is a block diagram showing an example of the functional configuration of a terminal according to an embodiment. FIG. 10 is a flowchart showing the operation of an AP in UL-OFDMA transmission. Fig. 11 is a flowchart showing the operation of each terminal in UL-OFDMA transmission. Fig. 12 is a timing chart showing the operation in UL-OFDMA transmission. Fig. 13 is a diagram showing the format of a Transmit Power Envelope element. Fig. 14 is a diagram showing an example of a multi-AP configuration.

[0011] Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a block diagram showing an example of the configuration of a communication system according to an embodiment. As shown in Fig. 1, the communication system 1 includes an access point (AP) 10, terminals 20-1, 20-2, ..., 20-N, and a network 30.

[0012] The AP 10 and the terminals 20-1, 20-2, ..., 20-N have wireless communication functions based on, for example, the OSI (Open Systems Interconnection) reference model. In the OSI reference model, wireless communication functions are divided into seven layers (Layer 1: Physical Layer, Layer 2: Data Link Layer, Layer 3: Network Layer, Layer 4: Transport Layer, Layer 5: Session Layer, Layer 6: Presentation Layer, and Layer 7: Application Layer). The data link layer includes a Logical Link Control (LLC) sublayer and a Media Access Control (MAC) sublayer.

[0013] The AP 10 and terminals 20-1, 20-2, ..., 20-N support UL-OFDMA transmission. Furthermore, the AP 10 and terminals 20-1, 20-2, ..., 20-N support DRUs (distributed RUs) that configure RUs using discretely allocated subcarriers during UL-OFDMA transmission. The DRUs will be described in detail later.

[0014] Terminals 20-1, 20-2, ..., 20-N are N terminals. N is a natural number, typically an integer equal to or greater than 2. Terminals 20-1, 20-2, ..., 20-N can exchange traffic with AP 10. Terminals 20-1, 20-2, ..., 20-N are, for example, smartphones or PCs (personal computers), and are wireless terminals conforming to the IEEE 802.11 standard. In the following, terminals 20-1, 20-2, ..., 20-N have the same configuration. In the following, when there is no particular need to distinguish between terminals 20-1, 20-2, ..., 20-N, they may be referred to as terminals 20.

[0015] Next, the hardware configuration of the AP and the terminal in the communication system according to the embodiment will be described.

[0016] 2 is a block diagram showing an example of the hardware configuration of an AP 10. As shown in FIG. 2, the AP 10 includes, for example, a central processing unit (CPU) 11, a read only memory (ROM) 12, a random access memory (RAM) 13, a wireless communication module 14, and a wired communication module 15.

[0017] The CPU 11 is a processing circuit that controls the overall operation of the AP 10. The ROM 12 is, for example, a non-volatile semiconductor memory. The ROM 12 stores programs and data for controlling the AP 10. The RAM 13 is, for example, a volatile semiconductor memory. The RAM 13 is used as a work area for the CPU 11. The wireless communication module 14 is a circuit used to send and receive data via wireless signals. The wireless communication module 14 is connected to an antenna. The wired communication module 15 is a circuit used to send and receive data via wired signals. The wired communication module 15 is connected to the network 30.

[0018] Although the wired communication module 15 is described as a means for connecting the AP 10 and the network 30, a wireless communication module different from the wireless communication module 14 may alternatively be used, or the wireless communication module 14 may communicate with the network 30 during times when it is not communicating with the terminal 20.

[0019] 3 is a block diagram showing an example of the hardware configuration of the terminal 20. As shown in FIG. 3, the terminal 20 includes, for example, a CPU 21, a ROM 22, a RAM 23, a wireless communication module 24, a display 25, and a storage 26.

[0020] The CPU 21 is a processing circuit that controls the overall operation of the terminal 20. The ROM 22 is, for example, a non-volatile semiconductor memory. The ROM 22 stores programs and data for controlling the terminal 20. The RAM 23 is, for example, a volatile semiconductor memory. The RAM 23 is used as a working area for the CPU 21. The wireless communication module 24 is a circuit used for transmitting and receiving data via wireless signals. The wireless communication module 24 is connected to an antenna. The display 25 is, for example, an LCD (liquid crystal display) or an EL (electro-luminescence) display. The display 25 displays a GUI (graphical user interface) corresponding to application software, etc. The storage 26 is a non-volatile storage device. The storage 26 stores system software, etc. of the terminal 20.

[0021] Next, the functional configuration of the AP and the terminal in the communication system according to the embodiment will be described.

[0022] 4 is a block diagram showing an example of the functional configuration of an AP according to an embodiment. The AP 10 functions as a computer including a data processing unit 110, a frame processing unit 120, a management unit 130, and a radio signal processing unit 140. The data processing unit 110 is a functional block that executes processing corresponding to the LLC sublayer of layer 2 and layers 3 to 7. The frame processing unit 120 and the management unit 130 are functional blocks that execute processing corresponding to the MAC sublayer of layer 2. The radio signal processing unit 140 is a functional block that executes processing corresponding to layer 1.

[0023] The data processing unit 110 outputs data input from the network 30 via the LLC layer to the frame processing unit 120. The data processing unit 110 also outputs data input from the frame processing unit 120 to the network 30 via the LLC layer.

[0024] When data is input to frame processing unit 120 from data processing unit 110 or management unit 130, frame processing unit 120 adds a MAC header to the input data to generate a MAC frame. Frame processing unit 120 then outputs the MAC frame to radio signal processing unit 140. When a MAC frame is input from radio signal processing unit 140, frame processing unit 120 extracts data from the MAC frame and outputs the extracted data to data processing unit 110 or management unit 130 depending on the type of MAC frame. Specifically, when the MAC frame is a data frame, frame processing unit 120 inputs the data to data processing unit 110. When the MAC frame is a management frame or a control frame, frame processing unit 120 inputs the data to management unit 130.

[0025] The management unit 130 controls the logical wireless connection between the AP 10 and the terminal 20. For example, the management unit 130 executes wireless connection processing in response to an association request from the terminal 20. The management unit 130 also has an OFDMA management unit 131. The OFDMA management unit 131 manages OFDMA transmission, such as notifying the terminal 20 of an upper limit of transmission power during OFDMA transmission, and allocating RUs and arranging subcarriers in accordance with the upper limit of transmission power and restrictions on the number of subcarriers per frequency.

[0026] As management information related to OFDMA transmission, the OFDMA management unit 131 stores maximum transmission power information 1311 and subcarrier allocation information 1312. Furthermore, as management information related to OFDMA transmission, the OFDMA management unit 131 can store information on a combination of RUs assigned to each terminal and information on the allocation of subcarriers for each RU.

[0027] The maximum transmission power information 1311 includes information on the maximum transmission power per subcarrier per bandwidth and per RU when a DRU is used, which is set based on the laws and regulations of the country in which the AP 10 is installed. In addition, the maximum transmission power information 1311 may include information on the maximum transmission power per subcarrier per bandwidth when a DRU is not used. Furthermore, the maximum transmission power information 1311 may include information on the maximum transmission power when OFDMA transmission is not used. The subcarrier allocation information 1312 is information on the combination of RUs for each frequency bandwidth and the conditions for subcarrier allocation for each RU. The maximum transmission power information 1311 and the subcarrier allocation information 1312 will be described in detail later.

[0028] The OFDMA management unit 131 notifies the terminal 20 of information on the maximum transmission power when using the DRU, based on the maximum transmission power information 1311. The notification can be performed using a notification frame such as a beacon frame or a trigger frame.

[0029] 5A is a diagram illustrating a first example of a broadcast frame. The broadcast frame of the first example includes, for example, a DRU enable / disable field and a maximum transmit power field for each bandwidth and each RU. In addition, the broadcast frame of the first example may include information on RU allocation for each terminal, etc.

[0030] The DRU enable / disable field is a field indicating information on whether the use of a DRU during OFDMA transmission is enabled or disabled. If the DRU enable / disable field is enabled, the DRU can be used during OFDMA transmission. If the DRU enable / disable field is disabled, the DRU is not used during OFDMA transmission, and normal OFDMA transmission is performed. Whether or not to use a DRU may be determined from other parameters or other signaling, without relying on the DRU enable / disable field. In this case, the broadcast frame of the first example may not include the DRU enable / disable field.

[0031] The maximum transmission power per bandwidth and per RU field indicates information about the upper limit power per subcarrier for each bandwidth and each RU used in OFDMA transmission. If the DRU enable / disable field is enabled, the maximum transmission power field stores the maximum transmission power for each bandwidth and each RU when a DRU is used. If the DRU enable / disable field is disabled, the maximum transmission power field stores the maximum transmission power when a DRU is not used. The terminal 20 can set the transmission power for OFDMA transmission within the range of the maximum transmission power indicated by the maximum transmission power field.

[0032] In this example, a method of notifying in advance whether or not to perform DRU is shown, but since there are situations where STAs that can only use RU and STAs that can also use DRU coexist, another method is to notify whether the notification is for RU or DRU when making an RU allocation notification using a trigger frame, and select whether to use RU or DRU each time UL-OFDMA transmission is performed.

[0033] 5B is a diagram showing a second example of a broadcast frame. The broadcast frame of the second example has, for example, an available DRU field in addition to a DRU enabled / disabled field and a maximum transmit power field for each bandwidth and each RU. In addition, the broadcast frame of the second example may include information on RU allocation for each terminal, etc. The DRU enabled / disabled field and the maximum transmit power field are the same as those stored in the broadcast frame of the first example.

[0034] The available DRU field indicates the DRUs available for OFDMA transmission, determined based on the maximum transmission power and number of subcarriers per bandwidth. The terminal 20 cannot perform OFDMA transmission using DRUs other than those indicated in the available DRU field. As in the first example, whether to use a DRU may be determined based on other parameters or other signaling, rather than on the DRU enabled / disabled field. In this case, the broadcast frame of the second example does not need to include the DRU enabled / disabled field.

[0035] 5C is a diagram showing a third example of a broadcast frame. The broadcast frame of the third example has, for example, a DRU enable / disable field, an RU assignment field, and a maximum transmit power field. The DRU enable / disable field is the same as that stored in the broadcast frame of the first example.

[0036] The RU allocation field is a field indicating information on RU allocation and subcarrier allocation for each terminal 20. The terminal 20 can perform OFDMA transmission by allocating OFDMA frames to the RUs specified by the RU allocation field.

[0037] The maximum transmission power field indicates the maximum transmission power per subcarrier when performing OFDMA transmission using the RU specified in the RU assignment field. The terminal 20 can perform OFDMA transmission within the range of the maximum transmission power specified by the maximum transmission power field. Here, the information stored in the DRU enable / disable field and the information stored in the RU assignment field indicates whether to use the maximum transmission power corresponding to the RU or the maximum transmission power corresponding to the DRU. Therefore, the broadcast frame in the third example does not need to have a maximum transmission power field.

[0038] The maximum transmission power information 1311 in the embodiment will be described below. FIG. 6 is a diagram showing an example of RU allocation in OFDMA transmission using a 20 MHz channel. Currently, the IEEE 802.11 standard defines a total of four patterns of RU allocation. Hereinafter, an RU consisting of m subcarriers will be referred to as mRU. For example, in the following, "26RU" means an RU consisting of 26 subcarriers.

[0039] For example, if the pattern shown in the second row from the top, which is one of the four RU allocation patterns shown in Figure 6, is used, simultaneous transmission by five terminals (STAs) is possible. Note that in Figure 6, one 26RU is composed of two sets of 13 subcarriers with a DC subcarrier in between, as shown as Middle-26-tone RU. The same applies to the other patterns.

[0040] In many countries, the laws and regulations governing frequency bands used by wireless LANs specify the upper limit of transmission power, defined as antenna power or equivalent isotropically radiated power (EIRP), as a power density per unit frequency band. The IEEE 802.11 standard defines a channel bandwidth as a minimum unit of 20 MHz. Therefore, upper limits of transmission power are specified for communications using a 20 MHz channel and for communications using 2, 4, 8, or 16 20 MHz channels, i.e., 40, 80, 160, or 320 MHz.

[0041] Figure 7 shows the upper limit of transmission power (transmission power density) in the 6 GHz band as specified by the Radio Law of Japan. As shown in Figure 7, upper limits of transmission power are specified in Japan for the 20 MHz, 40 MHz, 80 MHz, 160 MHz, and 320 MHz bands. In Japan, the upper limit of transmission power specified in Figure 7 must be observed. In other countries, the upper limit of transmission power specified in the laws and regulations of that country must also be observed. Note that in Japan, the number of subcarriers per 1 MHz is also specified. Therefore, in Japan, the number of subcarriers per 1 MHz must also be observed.

[0042] In UL-OFDMA transmission as defined in the IEEE 802.11ax and 11be standards, an RU is composed of consecutive subcarriers. The narrower the bandwidth of an RU, the lower the transmission power of the entire RU. For example, comparing the 26 RUs and 52 RUs shown in FIG. 6, the signal bandwidth of both 26 RUs and 52 RUs is 20 MHz or less. Therefore, in Japan, the upper limit of the transmission power for both 26 RUs and 52 RUs is 10 mW / MHz, as shown in FIG. 7.

[0043] Actual RUs also include pilot subcarriers for synchronization acquisition in some receivers and null subcarriers containing no signals. However, ignoring these for the sake of explanation, 26 RUs and 52 RUs are both frequency blocks composed of consecutive subcarriers. Therefore, if the same maximum power density is specified for 26 RUs and 52 RUs, the upper limit of the transmission power per subcarrier will be the same. Therefore, the maximum transmission power of the entire RU is the product of the transmission power per subcarrier and the number of subcarriers in the RU used by the terminal performing transmission. Therefore, when comparing 26 RUs and 52 RUs, the transmission power of 26 RUs is lower. The use of DRUs is being considered to ensure successful transmission even with RUs with a smaller number of subcarriers.

[0044] 8A and 8B are diagrams showing the RU placement defined in the IEEE 802.11ax / be standard and the RU placement when using the DRU concept proposed in IEEE 802.11TGbn for UL-OFDMA transmission using a 20 MHz channel. (a) of FIG. 8 shows the RU placement defined in the IEEE 802.11ax / be standard. (b) of FIG. 8 shows the RU placement when using the DRU concept proposed in IEEE 802.11TGbn. In FIG. 8, the placement of pilot subcarriers and null subcarriers is omitted for simplicity of explanation.

[0045] As shown in (a) of Figure 8, in the IEEE 802.11ax / be standard, an RU is configured with a group of consecutive subcarriers on the frequency axis. In this specification, the subcarrier spacing is 78.125 kHz, so the number of subcarriers included per 1 MHz width is 13 (=ceiling (1 MHz / 78.125 kHz)). Therefore, as shown in Figure 7, if the maximum power density in a 20 MHz channel is 10 dBm / MHz (=10 mW / MHz), the maximum transmission power per subcarrier is -1.1 dBm / MHz (=10 dBm / MHz - 10 log), regardless of the number of subcarriers that make up the RU. １０ 13).

[0046] In contrast, in the DRU proposed in IEEE 802.11TGbn, as shown in FIG. 8(b), the subcarriers constituting the RU are distributed across the entire band in which UL-OFDMA is performed. The example in FIG. 8(b) shows an example of an even subcarrier distribution in a combination of four 52RUs and one 26RU. In other words, the subcarriers of each RU are arranged in a comb-like pattern so as to be spread across the entire 20 MHz channel. Since a DRU can have a mixture of 52RUs and 26RUs, if the kth subcarrier from the left of RU number n (n = 1, 2, 3, 4, 5) in FIG. 8(b) is written as SC{n, k}, then the subcarrier distribution when using a DRU in the example in FIG. 8(b) is as follows: SC{1,1}, SC{2,1}, SC{3,1}, SC{4,1}, SC{5,1}, SC{1,2}, SC{2,2}, SC{4,2},SC{5,2}, SC{1,3}, SC{2,3}, SC{3,2}, SC{4,3},SC{5,3}, SC{1,4}, SC{2,4}, SC{4,4}, SC{5,4}, ......, SC{1,51}, SC{2,51}, SC{3,26}, SC{4,51}, SC{5,51}, SC{1,52}, SC{2,52}, SC{4,52}, SC{5,52}

[0047] The number of subcarriers in 26RU-3 is half that of 52RU-1, 2, 4, and 5. Therefore, in Fig. 8(b), subcarriers are arranged every other subcarrier in Fig. 26RU-3. The arrangement of subcarriers in the DRU is not limited to that shown in Fig. 8(b).

[0048] Now, focusing on 52RU-1, the subcarriers of 52RU-1 are spread across the entire 20 MHz, and are arranged as follows. Here, "blank" means a subcarrier that does not emit a signal. SC{1,1}, blank, blank, blank, blank, SC{1,2}, blank, blank, blank, SC{1,3}, blank, blank, blank, blank, SC{1,4}, blank, blank, blank, ......, SC{1,51}, blank, blank, blank, blank, SC{1,52}, blank, blank, blank

[0049] By arranging the RUs as DRUs, the subcarrier spacing is expanded. And because the subcarrier spacing is expanded, the number of subcarriers per 1 MHz is reduced. In the case of 52RU-1, the number of subcarriers per 1 MHz channel is reduced to a maximum of three. Therefore, the maximum transmission power per subcarrier for 52RU-1 is 5.2 dBm / MHz (= 10 dBm / MHz - 10 log １０ The same applies to the maximum transmission power per subcarrier of 52RU-2, 52RU-4, and 52RU-5.

[0050] In this way, by arranging 52 RUs in the DRU arrangement shown in FIG. 8B, the transmission power can be increased by a maximum of 6.3 dB even under the condition that the upper limit of the transmission power is observed.

[0051] Furthermore, looking at 26RU-3, the subcarriers of 26RU-3 are spread across the entire 20 MHz band and are arranged as follows: blank, blank, SC{3,1}, blank, blank, blank, blank, blank, blank, blank, blank, blank, SC{3,2}, blank, blank, blank, blank, blank, blank, ......, blank, blank, SC{3,26}, blank, blank, blank, blank, blank, blank, blank

[0052] If the subcarriers constituting the 26RU are arranged as shown in FIG. 8B, the number of subcarriers per 1 MHz channel will be reduced to a maximum of two. Therefore, the maximum transmission power per subcarrier of the 26RU-3 will be 7.0 dBm / MHz (= 10 dBm / MHz - 10 log １０ 2).

[0053] In this way, by arranging 26 RUs in the DRU arrangement shown in FIG. 8B, the transmission power can be increased by a maximum of 8.1 dB even under the condition that the upper limit of the transmission power is observed.

[0054] In this way, when RUs are arranged as DRUs, the transmission power per subcarrier can be higher than when RUs are not arranged as DRUs. On the other hand, with DRUs, the maximum transmission power may vary depending on the RUs assigned and the arrangement of subcarriers. Therefore, in the embodiment, information on the upper limit of the maximum transmission power for each bandwidth and each RU is managed as maximum transmission power information 1311, taking into consideration the use of DRUs. The information on the upper limit of the maximum transmission power may be managed as an absolute value, or may be managed as a relative value to the upper limit of transmission power for each bandwidth specified by laws and regulations, etc., with respect to the case where conventional RUs or UL-OFDMA are not used. For example, the absolute value of the maximum transmission power for 52 RUs with the subcarrier arrangement of (b) in FIG. 8 on a 20 MHz channel is 5.2 dBm / MHz when conventional RUs or UL-OFDMA are not used. On the other hand, the relative value when DRUs are used is 4.8 (=10 log １０3) MHz. The absolute value of the maximum transmission power of 26 RUs with the subcarrier arrangement of FIG. 8(b) in a 20 MHz channel is 7.0 dBm / MHz. On the other hand, the relative value is 3.0 (=10 log １０ 2) MHz. Based on the maximum transmission power information 1311 transmitted from the AP 10, the terminal 20 can perform OFDMA transmission using the maximum transmission power DRU within the legally compliant range.

[0055] Furthermore, in the subcarrier allocation shown in FIG. 8(b), the number of subcarriers per 1 MHz is two. On the other hand, as shown in FIG. 7, the upper limit of transmission power in Japan tends to be lower as the frequency band increases. Therefore, in the case of a DRU, particularly when a high frequency band is used, the number of subcarriers per 1 MHz may be less than one depending on how the DRU is allocated and how the subcarriers are allocated. In Japan, laws and regulations stipulate that the number of subcarriers per 1 MHz must be one or more, and this regulation must be observed. Therefore, if there is a regulation regarding the number of subcarriers per frequency, that information is managed as subcarrier allocation information 1312. Based on the subcarrier allocation information 1312, the AP 10 and the terminal 20 can perform OFDMA transmission using a DRU by allocating subcarriers with a number of subcarriers that complies with the law.

[0056] Furthermore, the regulations for the maximum transmission power and the number of subcarriers per frequency vary from country to country. If the AP 10 is a portable AP, it may be used in multiple countries. The AP 10 may manage maximum transmission power information 1311 and subcarrier allocation information 1312 corresponding to the regulations of each country so that the AP 10, which may be used in multiple countries, can transmit information on the maximum transmission power and the number of subcarriers per frequency specified by the laws and regulations of each country to the terminal 20. Alternatively, the AP 10 may acquire the maximum transmission power information 1311 and subcarrier allocation information 1312 corresponding to the regulations of each country in each country, for example, via the network 30.

[0057] Returning now to the description of FIG. 4 , the radio signal processing unit 140 generates a radio frame by adding a preamble and the like to the MAC frame input from the frame processing unit 120. The radio signal processing unit 140 converts the generated radio frame into a radio signal. The radio signal processing unit 140 then radiates (transmits) the converted radio signal via an antenna. The radio signal processing unit 140 may also assign and transmit the OFDMA frame to subcarriers based on the RU or DRU assignment. The radio signal processing unit 140 may also transmit a trigger frame for UL-OFDMA transmission. This trigger frame may include fields for storing the transmission power information and available DRU information shown in FIGS. 5A-5C. The conversion process from the radio frame to the radio signal includes, for example, convolutional coding, interleaving, subcarrier modulation, inverse fast Fourier transform, OFDM modulation, and frequency conversion. The radio signal processing unit 140 also converts the radio signal received via the antenna into a radio frame. The radio signal processing unit 140 extracts a MAC frame from the converted radio frame, and then outputs the extracted MAC frame to the frame processing unit 120. The conversion process from the radio signal to the radio frame includes, for example, frequency conversion, OFDM demodulation, fast Fourier transform, subcarrier demodulation, deinterleaving, and Viterbi decoding.

[0058] 9 is a block diagram showing an example of the functional configuration of a terminal according to an embodiment. The terminal 20 functions as a computer including a data processing unit 210, a frame processing unit 220, a management unit 230, a radio signal processing unit 240, and an application execution unit 250. The data processing unit 210 and the application execution unit 250 are functional blocks that execute processes corresponding to the LLC sublayer of layer 2 and layers 3 to 7. The frame processing unit 220 and the management unit 230 are functional blocks that execute processes corresponding to the MAC sublayer of layer 2. The radio signal processing unit 240 is a functional block that executes processes corresponding to layer 1.

[0059] The data processing unit 210 outputs data input from the application execution unit 250 via the LLC layer to the frame processing unit 220. The data processing unit 210 also outputs data input from the frame processing unit 220 to the application execution unit 250 via the LLC layer.

[0060] When data is input to frame processing unit 220 from data processing unit 210 or management unit 230, frame processing unit 220 adds a MAC header to the input data to generate a MAC frame. Frame processing unit 220 then outputs the MAC frame to radio signal processing unit 240. When a MAC frame is input from radio signal processing unit 240, frame processing unit 220 extracts data from the MAC frame and outputs the extracted data to data processing unit 210 or management unit 230 depending on the type of MAC frame. Specifically, when the MAC frame is a data frame, frame processing unit 220 inputs the data to data processing unit 210. When the MAC frame is a management frame or a control frame, frame processing unit 220 inputs the data to management unit 230.

[0061] The management unit 230 controls the logical wireless connection between the terminal 20 and the AP 10. For example, the management unit 230 generates an association request based on a beacon frame from the AP 10. The management unit 230 also includes an OFDMA management unit 231. The OFDMA management unit 231 manages OFDMA transmission, such as allocating RUs and allocating subcarriers in accordance with the maximum transmission power limit notified by the AP 10 during OFDMA transmission. The OFDMA management unit 231 stores maximum transmission power information and subcarrier allocation information notified by the AP 10 as management information related to OFDM transmission. Furthermore, the OFDMA management unit 231 may store information on the combination of RUs allocated to each terminal and information on the allocation of subcarriers for each RU as management information related to OFDMA transmission.

[0062] The radio signal processing unit 240 generates a radio frame by adding a preamble and the like to the MAC frame input from the frame processing unit 220. The radio signal processing unit 240 converts the generated radio frame into a radio signal. The radio signal processing unit 240 then radiates (transmits) the converted radio signal via an antenna. The radio signal processing unit 240 may also assign the OFDMA frame to subcarriers based on the RU or DRU assignment and transmit the subcarriers. The conversion process from the radio frame to the radio signal includes, for example, convolutional coding, interleaving, subcarrier modulation, inverse fast Fourier transform, OFDM modulation, and frequency conversion. The radio signal processing unit 240 also converts the radio signal received via the antenna into a radio frame. The conversion process from the radio signal to the radio frame includes, for example, frequency conversion, OFDM demodulation, fast Fourier transform, subcarrier demodulation, deinterleaving, and Viterbi decoding. The radio signal processing unit 240 extracts a MAC frame from the converted radio frame. Then, the radio signal processing unit 240 outputs the extracted MAC frame to the frame processing unit 220 .

[0063] The application execution unit 250 executes an application based on data input from the data processing unit 210. The application execution unit 250 also inputs data to the data processing unit 210. For example, the application execution unit 250 can display application information on the display 25. The application execution unit 250 can also operate based on operations on an input interface.

[0064] Next, the UL-ODFDMA transmission operation in the communication system according to the embodiment will be described. FIG. 10 is a flowchart showing the operation of the AP 10 in UL-OFDMA transmission. Here, it is assumed that, prior to the operation of FIG. 10, the AP 10 performs a CCA (Clear Channel Assessment) operation and confirms that the channel used for UL-OFDMA transmission is not in use. It is also assumed that N terminals 20 are wirelessly connected to the AP 10. Information on the maximum transmission power when using the DRU may be reported to these N terminals 20 by transmitting a beacon frame or the like. A beacon frame including the information shown in FIG. 5A or 5B may be used as the beacon frame for reporting the information on the maximum transmission power.

[0065] In step S11, the AP 10 transmits a trigger frame to each terminal 20 using the radio signal processing unit 140. This trigger frame is transmitted to synchronize the timing of radio signals from each terminal 20 belonging to a member performing OFDMA transmission and to notify the AP 10 of the target value of the received power of the signal transmitted by the terminal 20. The trigger frame also includes at least information indicating the terminal 20 of the member performing OFDMA transmission, information on the RU allocation and subcarrier placement of each terminal 20 of the member, and information on the maximum transmission power. For example, a trigger frame including the information shown in FIG. 5C can be used as this trigger frame.

[0066] In step S12, the AP 10 determines whether or not it has received a wireless signal including a data frame (OFDMA frame) from each terminal 20. In step S12, the AP 10 waits until it receives a wireless signal including a data frame from each terminal 20. If a wireless signal including a data frame is received from each terminal 20 in step S12, the AP 10 transitions the process to step S13. Note that if the AP 10 has not received a wireless signal within a predetermined period of time, it transitions to a processing end state.

[0067] In step S13, the AP 10 checks whether the data frames received from each terminal 20 have been received correctly, and transmits the check result to each terminal 20 as a block ACK (BACK). The process in FIG. 10 then ends. Depending on the result of the BACK, retransmission processing or the like may be performed. The retransmission processing is omitted in FIG. 10. The AP 10 may also perform various processing depending on the data frames received from each terminal 20. Processing depending on the data frames is also omitted in FIG. 10.

[0068] FIG. 11 is a flowchart showing the operation of each terminal 20 in UL-OFDMA transmission.

[0069] In step S21, the terminal 20 determines whether a trigger frame has been received. In step S21, the terminal 20 waits until the trigger frame is received. If the trigger frame is not received within a predetermined period or if a frame other than the trigger frame is received, the terminal 20 may proceed to processing of that frame and end the processing of FIG. 11. Furthermore, even if the trigger frame is received, the processing of FIG. 11 also ends if the terminal 20 is not included in the members that perform OFDMA transmission. In step S21, if the trigger frame is received and the terminal 20 is included in the members, the terminal 20 proceeds to step S22.

[0070] In step S22, the terminal 20 updates the RU allocation information and subcarrier allocation information managed by its own OFDMA management unit 231 based on the RU allocation information and subcarrier allocation information contained in the received trigger frame.

[0071] In step S23, the terminal 20 sets the transmission power for each subcarrier based on the information on the maximum transmission power per subcarrier included in the received trigger frame and the target value of the reception power at the AP 10 of the signal transmitted by the terminal 20. The terminal 20 can set the transmission power within a range in which the transmission power per subcarrier does not exceed the maximum transmission power.

[0072] In step S24, after waiting a predetermined interval from the trigger frame, the terminal 20 transmits a wireless signal including a data frame (OFDMA frame) using the wireless signal processing unit 240. The predetermined interval is, for example, SIFS (Short Inter Frame Space). Furthermore, the transmission power during OFDMA transmission is set within a range in which the transmission power per subcarrier does not exceed the maximum transmission power notified by the AP 10. The transmission power of the wireless signal from the terminal 20 can be maximized while complying with laws and regulations. By maximizing the transmission power, the probability of successful transmission is increased even for RUs with a small number of subcarriers.

[0073] In step S25, the terminal 20 receives BACK from the AP 10. In step S25, if the terminal 20 receives BACK from the AP 10, it considers that the data frame it transmitted has been delivered. In step S25, if the terminal 20 cannot confirm receipt of BACK, it considers that the data frame it transmitted has not been delivered. By performing either of these confirmations, the processing in FIG. 11 ends. Here, depending on the result of the BACK, retransmission processing or the like is performed. In FIG. 11, the retransmission processing is omitted.

[0074] 12 is a timing chart showing the operation of UL-OFDMA transmission. After the CCA operation by the AP 10, the AP 10 notifies the reservation of UL-OFDMA transmission by transmitting a trigger frame. This trigger frame includes at least information indicating the member terminals 20 that will perform OFDMA transmission, information on the RU allocation and subcarrier placement of each member terminal 20, and information on the maximum transmission power.

[0075] Each terminal 20 that receives the trigger frame and is included in the members of the UL-OFDMA transmission assigns an OFDMA frame to the RU assigned to itself, and then transmits a data frame at a predetermined frame interval (usually SIFS: Short Inter Frame Space) from the trigger frame. The transmission power at this time is set within a range that does not exceed the maximum transmission power per subcarrier notified by the beacon frame or trigger frame.

[0076] When the AP 10 receives a wireless signal from each terminal 20 , it transmits a BACK to each terminal 20 .

[0077] As described above, according to the embodiment, the AP 10 broadcasts information about the maximum transmission power per subcarrier per bandwidth and per RU when using a DRU to members performing UL-OFDMA transmission. This allows the terminal 20 to perform OFDMA transmission using a DRU at the maximum transmission power within the scope of legal regulations, even if the terminal 20 does not possess this information itself. Furthermore, while the information about the maximum transmission power per subcarrier per bandwidth and per RU when using a DRU is created based on the information about the maximum transmission power stipulated by legal regulations, the information about the maximum transmission power per subcarrier when using a DRU is managed separately from the information about the maximum transmission power per subcarrier in a transmission mode when a DRU is not used. This ensures compliance with legal regulations even if there are different maximum transmission power restrictions when using a DRU and when not using a DRU.

[0078] Furthermore, if the AP 10 is portable, it can accommodate changes in the country in which it is used by storing or externally acquiring information on the maximum transmission power per subcarrier for each bandwidth and each RU and the number of subcarriers per frequency that correspond to each country. For example, the AP 10 may store information specified by the laws and regulations of each country in advance, or may be able to obtain or reference it via an external connection. Furthermore, the AP 10 may operate to remove restrictions depending on the country to which it connects.

[0079] (Modification) A modification of the embodiment will be described below. In the embodiment, a beacon frame, a trigger frame, etc., which are provided with a dedicated field for storing information on the maximum transmit power per subcarrier for each bandwidth and each RU, are transmitted to the terminal 20. In contrast, the IEEE 802.11 baseline standard defines a Transmit Power Envelope element for notifying the upper limit of the transmit power. The terminal 20 may set the transmit power by using this Transmit Power Envelope element.

[0080] Fig. 13 is a diagram showing the format of the Transmit Power Envelope element. As shown in Fig. 13, the Transmit Power Envelope element has a Local Maximum Transmit Power field for storing the value of the upper limit power when communication is performed at 40, 80, 160, or 320 MHz. This field typically stores the upper limit value of the transmit power specified by laws and regulations, etc., as shown in Fig. 7. As a modified example of the embodiment, the upper limit value of the transmit power for each bandwidth stored in the Transmit Power Envelope element may be transmitted from the AP 10 to the terminal 20, and the terminal 20 may calculate the maximum transmit power per subcarrier for each bandwidth and for each RU based on this stored upper limit value of the transmit power for each bandwidth and the RU allocation information and subcarrier placement information notified by the AP 10.

[0081] In the embodiment, there is one AP. Here, in IEEE 802.11TGbn, multi-AP, which performs transmission by cooperating with multiple APs, is being studied. Furthermore, Co-OFDMA, which performs OFDMA transmission between multiple APs, is also being studied in the multi-AP study. The technology of the embodiment can also be applied to Co-OFDMA.

[0082] 14 is a diagram showing an example of the configuration of a multi-AP. In this example of the multi-AP, M shared APs 10-1, ..., 10-M are wirelessly connected to one sharing AP 40 connected to a network 30. M is a natural number, typically an integer of 2 or greater. For example, terminals 20-1 and 20-2 are wirelessly connected to the shared AP 10-1, and for example, terminal 20-N is wirelessly connected to the shared AP 10-2 (corresponding to M=2 in FIG. 14).

[0083] The shared APs 10-1 and 10-2 can wirelessly communicate with terminals belonging to each of them using overlapping channels. In uplink Co-OFDMA, terminals belonging to the shared AP 10-1 and the shared AP 10-2 share RUs for transmission. RU allocation and subcarrier allocation can be performed, for example, by the sharing AP 40. Furthermore, the sharing AP 40 manages the information on the maximum transmission power per subcarrier and the number of subcarriers per frequency for each bandwidth and each RU. The sharing AP 40 can then report the information on the maximum transmission power and the number of subcarriers per frequency to the shared APs 10-1 and 10-2 under its control using beacon frames, etc. As a result, the shared AP 10-1 and the shared AP 10-2 can report the information on the maximum transmission power and the number of subcarriers per frequency to the terminals belonging to each of them.

[0084] In the embodiment, the application to OFDMA transmission using a DRU in uplink is described. On the other hand, the technology of the embodiment can also be applied to OFDMA transmission using a DRU in downlink. In this case, the AP 10 sets the transmission power based on information managed by itself and performs OFDMA using the DRU.

[0085] The processing in AP 10 can also be stored as a program that can be executed by a processor, which is a computer. Alternatively, the processing can be stored and distributed in a storage medium of an external storage device such as a magnetic disk, optical disk, or semiconductor memory. Each processor in AP 10 can then load the program stored in the storage medium of the external storage device and execute various processes by having its operation controlled by the loaded program.

[0086] The present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the embodiments may be implemented in appropriate combinations, in which case the combined effects can be obtained. Furthermore, the above-described embodiments include various inventions, and various inventions can be extracted by combining selected elements from the disclosed elements. For example, if the problem can be solved and the desired effect can be obtained even if some elements are deleted from all elements shown in the embodiments, the configuration from which these elements are deleted can be extracted as an invention.

[0087] DESCRIPTION OF SYMBOLS 1...Communication system 10...Access point (AP) 10-1, 10-2...Sharing AP 11...CPU 12...ROM 13...RAM 14...Wireless communication module 15...Wired communication module 20, 20-1, 20-2...Terminal 21...CPU 22...ROM 23...RAM 24...Wireless communication module 25...Display 26...Storage 30...Network 40...Sharing AP 110...Data processing unit 120...Frame processing unit 130...Management unit 131...OFDMA management unit 140...Wireless signal processing unit 210...Data processing unit 220...Frame processing unit 230...Management unit 231...OFDMA management unit 240...Wireless signal processing unit 250...Application execution unit

Claims

1. An access point comprising: a radio signal processing unit that communicates with a plurality of terminals by discretely allocating a plurality of subcarriers for each allocated resource unit (RU); and a management unit that manages information on maximum transmission power for each RU and for each bandwidth to which the subcarriers belong, wherein the radio signal processing unit transmits the information on maximum transmission power for each RU and for each bandwidth to which the subcarriers belong to the terminal prior to communication with the terminal.

2. The access point according to claim 1, wherein the management unit allocates the RUs in a subcarrier arrangement that complies with laws and regulations.

3. The access point according to claim 1, wherein the management unit manages the maximum transmission power for each RU and for each bandwidth to which the subcarriers belong as an absolute value.

4. The access point according to claim 1, wherein the management unit manages the maximum transmission power for each RU and for each bandwidth to which the subcarriers belong as a relative value to an upper limit of transmission power for each bandwidth set by law.

5. A terminal comprising: a radio signal processing unit that communicates with an access point by discretely allocating multiple subcarriers for each allocated resource unit (RU); and a management unit that sets the transmission power in the radio signal processing unit based on information on the maximum transmission power for each RU and for each bandwidth to which the subcarriers belong, which information is notified from the access point.

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